From: "Omer Frenkel" <ofren...@redhat.com>
To: "Mike Kolesnik" <mkole...@redhat.com>
Cc: "engine-devel" <engine-devel@ovirt.org>
Sent: Sunday, December 1, 2013 11:09:32 AM
Subject: Re: [Engine-devel] Using config values
From: "Mike Kolesnik" <mkole...@redhat.com>
To: "Omer Frenkel" <ofren...@redhat.com>
Cc: "Kanagaraj" <kmayi...@redhat.com>, "engine-devel"
<engine-devel@ovirt.org>
Sent: Sunday, December 1, 2013 11:01:50 AM
Subject: Re: [Engine-devel] Using config values
From: "Mike Kolesnik" <mkole...@redhat.com>
To: "Kanagaraj" <kmayi...@redhat.com>
Cc: "engine-devel" <engine-devel@ovirt.org>
Sent: Sunday, December 1, 2013 8:08:42 AM
Subject: Re: [Engine-devel] Using config values
Hi All,
Hi Kanagaraj,
The are some issues arising in configurations whenever we move up on the
versions(3.3 => 3.4), because of the way we store and interpret them.
Whenever there is a new cluster level, you will need to add a new entry for
all(most) of the configuration. Mostly a copy paste if you see from 3.2 to
3.3, except some CPU/PM type related configurations.
Better option would be to have the defaul config value in ConfigValues.java
and the overrides will go to config.sql. In this approach you don't need a
new entries to config.sql when there is a new cluster level.
Lets take an exmaple, "SupportForceCreateVG" - This is supported from 3.1
onwards,
If you look at config.sql, you will see following entries
select fn_db_add_config_value('SupportForceCreateVG','false','3.0');
select fn_db_add_config_value('SupportForceCreateVG','true','3.1');
select fn_db_add_config_value('SupportForceCreateVG','true','3.2');
select fn_db_add_config_value('SupportForceCreateVG','true','3.3');
And in ConfigValues.java
@TypeConverterAttribute(Boolean.class)
@DefaultValueAttribute("false")
SupportForceCreateVG,
Now if there is 3.4 and 3.5, the user needs to add 2 more entries, which i
feel is redundant.
Instead we can make
@TypeConverterAttribute(Boolean.class)
@DefaultValueAttribute("true")
SupportForceCreateVG,
and have only the following in config.sql
select fn_db_add_config_value('SupportForceCreateVG','false','3.0');
if a particular value(for a specific cluster level) is not found in
Config.sql, the fallback is to use the value available in ConfigValues.java.
This has already been implemented, there are many "feature supported"
configurations working like this (for example GlusterSupport).
I think a more interesting approach would be to move these out of the DB
since these values don't really hav e a reson to be there.
Since the entire thing is abstracted by "Gluster/FeatureSupported" classes
then we can easily change mechanism (of course whatever code is not using it
can be easily converted to use the mechanism)
For example a simple enum could do the trick:
------------------------------------- EXAMPLE
-------------------------------------
/**
* Convenience class to check if a gluster feature is supported or not in any
given version.<br>
* Methods should be named by feature and accept version to check against.
*/
public class GlusterFeatureSupported {
/**
* @param version
* Compatibility version to check for.
* @return <code>true</code> if gluster support is enabled, <code>false</code>
if it's not.
*/
public static boolean gluster(Version version) {
return SupportedFeatures.GLUSTER.isSupportedOn(version);
}
/**
* @param version
* Compatibility version to check for.
* @return <code>true</code> if gluster heavyweight refresh is enabled,
<code>false</code> if it's not.
*/
public static boolean refreshHeavyWeight(Version version) {
return SupportedFeatures.REFRESH_HEAVYWEIGHT.isSupportedOn(version);
}
/* More methods... */
enum SupportedFeatures {
GLUSTER(Version.v3_0),
REFRESH_HEAVYWEIGHT(Version.v3_0, Version.v3_1),
/* More members */;
private Set<Version> unsupportedVersions = new HashSet<Version>();
private SupportedFeatures(Version... versions) {
unsupportedVersions.addAll(Arrays.asList(versions));
}
public boolean isSupportedOn(Version version) {
return !unsupportedVersions.contains(version);
}
}
------------------------------------- END EXAMPLE
-------------------------------------
Thoughts?
unless i didn't understand something, this is not good,
this should stay configurable by the users,
for example if some user experience some issues with a feature and want to
turn it off/change the values..
(not all version configuration are boolean, some are different values to
different versions, like cpu-list)
This is for API level compatibility.
If VDSM doesn't support for example hot plug in 3.1 then the user can't just
decide that it does and change it.
Also, this is not changeable by user since it's not exposed by engine-config
(nor should it be).
some are exposed
This is strictly for the engine-VDSM API compatibility, not for other configs
which are version specific.
right, but still user should be able to turn features off in case of
problems,
or change in some cases (for example it is possible to add support for more
power management devices, i know it was done by users)
no reason to block this
